Rattly bike chain

Bought a new Carrera bike from Halfords today. Assembled it myself. Took it for test ride. Great for a couple of miles, then the gears became all rattly. Tried adjusting them as the manual instructs, but I can't get it right.

I'm going to phone them up tomorrow night and ask for advice, but I imagine I'll end up taking it to pieces and driving it back to the store for whatever needs doing (my car is small!).

Any advice on how to remedy this myself? This is the bike in question btw.......

New bikes usually need adjusting slightly.If the gears aren't engaging fully (clicking) then the indexing is slightly out.Have you checked the front sprocket changer adjustment, it's easy to miss a problem there.But if there is a rattling noise, something is loose, or broken, possibly a problem with the Cassette, which needs specialised tools, so return it to Halfords.Halfords are reasonable and if their mechanic is any good, should be able to repair it while you wait.

but it could be the rattling noise is caused by a mis-alignment of the chain, where it is trying to climb onto the next gear sprocket. Unless some guide component of the gearing itself is mis-aligned, then I would say it has to be the adjustment that's at fault. Getting it right straight away can be tricky and fine adjustments, up or down, should clear it. TC.

Took it to Halfords on Monday, and they adjusted the gears (and brakes) there and then. Took it for a ride on Tuesday, and all's well, apart from the first seven gears. They're still rattly, lol, but I can manage without them. Probably. I can manage the few hilly bits in 2-3 or whatever.

Very light bike. Very comfy, too! Much more enjoyable experience than my old Raleigh Ogre mountain bike. That was too heavy for me, really.